G-171-0-C8641-A HQ-1009 Printed in Japan (MDOC)New publication, effective Sep. 2010

Specifications are subject to change without notice.

Power System Stabilizer (PSS)

Improper use of the products can cause severe injury or death,and may result in damage to the products and other property.Please read the instruction manual before installing or using the products.

Mitsubishi Electric Power System Stabilizer (PSS)

Gen

erat

or p

ower PSS OFF PSS ON

PSS OFF PSS ON

Time (sec)

Time (sec)

0.85

0.9

0.95

Gen

erat

or p

ower

0.85

0.9

0.95

0 1 2

0 1 2

Step response

Grid one line open

HEAD OFFICE: TOKYO BUILDING, 2-7-3, MARUNOUCHI, CHIYODA-KU, TOKYO 100-8310, JAPAN

AVR

AVR+

PSS

K1

K1+K1A

K1A+DA

K1+D

K1+D

K1+K1A+K1P

Tm

Tm

Tm

01Ms

1Ms

1Ms

S

0S

0S

D 0

0

0

D+DA

D+DA+DP

G

Power

Mitsubishi Power System Stabilizer (PSS)The power system stabilizer (PSS) is a device that measures improvements in system stability when added to a generators automatic voltage regulator (AVR). Therefore, compared to system reconstruction or enhancement, it offers overwhelmingly superior cost performance. With an abundant system line-up including analogue, digital and P//f input type models, Mitsubishi Electric is ready to respond to the diversified needs of its customers.

Summary of Power System Stability

Theory of PSS

Summary

Explanation of torque vector

Though generator output power is decided by a turbines mechanical torque, it can be changed by transiently changing the excitation value (Fig.1). A PSS detects the change in generator output power, controls the excitation value, and reduces the rapid power fluctuation (Fig.2).

Generator output power

Excitation value

Generator output power

Excitation value

Fault (3-phase fault, several cycles open)

Unstable (less dynamic stability)

StableStep out (less transient stability)

Fault

occu

rrenc

eFa

ult cl

eare

d

Transient area

Dynamic area

Constant excitation

Block diagram Torque characteristics

K1 : Synchronizing torqueD : Damping torqueM : Inertia

K1A : Synchronizing torque by AVRDA : Damping torque by AVR

K1P : Synchronizing torque by PSSDP : Damping torque by PSS

(Damping torque)

(Synchronizing torque)

Resultant torque

Resultant torque

(Unstable at DDA0)

(Stable at DDADP0)

1 2

Time

Power

By changing the excitation value, generator output power can be changed transiently

(Fig.1) (Fig.2)

A PSS detects the change ingenerator output power, controls the excitation value, and reduces the rapid power fluctuation

Vref

Vref

Vref

PT

PT

PT

CT

EXC

EXC

EXC

AVR

AVR

AVR

PSS

f PSS

P PSS

PSS

f PSS

P PSS

3 4

Mitsubishi Power System Stabilizer (PSS)

As previously mentioned, the PSS detects fluctuations in generator output power and controls the excitation. The type of PSS is distinguished by its detection signal. The simplest and most typical type is the P input type unit; however, and f input typeunits have been introduced to improve the stability of the intra-system oscillation mode (i.e., long-term or interface mode) in view of thelarge increase in power systems and power re-routing in recent years. Each of the features is outlined below.

Multi-input PSS

P signal

orf signal

Gain and phasecompensation

Gain and phasecompensation

Limiter

AVR

Local Mode Power Oscillation

Inter-area(Long-cycle) Mode Power Oscillation

Complex Power Oscillation

Individual generator oscillates against the systemFrequency is approx. 1Hz

The whole system oscillates as a resultof long-distance, large-capacity power transmissionFrequency is 0.2 to 0.5Hz

Complex power oscillation mode, such as local mode inter-area mode

Single-frequency PSS, such as P, or fP type PSS is more effective

Single-frequency PSS, such as P, or f or f type PSS is more effective

Multi-input PSS is more effectiveP type or Pf type

Types of PSS

Kpss Trs1+Trs1+Tlead1s1+Tlag1s

1+Tlead2s1+Tlag2s

1+Tlead3s1+Tlag3s 1+Tlags

1

Kpss Trs1+Trs1+Tlead1s1+Tlag1s

1+Tlead2s1+Tlag2s

1+Tlead3s1+Tlag3s

P1P2

T

Hardware Configuration

DevicePower/VoltageconverterPSS main card(SPMT)

PSS auxiliary card(SPST)

PSS protection card(SPPT)

FunctionDetects generator power and voltage from PT, CT signalAmplifier (Gain) [Kpss]Reset filter [Tr]Lag [Tlag]Limiter

Lead/Lag1 [Tlead1,Tlag1]Lead/Lag2 [Tlead2,Tlag2]Deadband, absolute

Low-power detection

Generator over-and under-voltagedetectionFault detection

PSS ON/OFF switching circuit

SpecificationPower converter: 0-1kW/0-30mV, response time: less than 10msec,voltage converter: 0-150VAC/0-5VDCKpss=0.13.0pu/pu (typical range)Tr=120secTlag=0.011secSetting range 0.1pu based on generator voltageStandard setting 0.05puTlead 1=0.082.2sec, Tlag 1=0.072.2secTlead 2=0.0080.22sec, Tlag 2=0.0070.22secSetting range 0-1pu based on generator outputStandard setting 0.3puSetting range 0-1pu based on generator outputStandard setting 0.3puSetting range 0-1.3pu based on generator voltageStandard setting over voltage: 1.1pu, under-voltage: 0.9puDetects PSS output that is over a set value/timeSetting range pick up: 0.1pu based on generator voltagetimer: 0-30secStandard setting0.045pu, 10secAutomatic lock (OFF) and automatic reset (ON) by low power detection,Generator over- and under-voltage detectionAutomatic lock (OFF) and manual reset (ON) by fault detection

Transfer function

Gain Reset filterDeadband Lead/Lag(1) Lead/Lag(2) Lead/Lag(3) Lag Limiter

Remarks) If Lead/Lag (3) is necessary, two PSS auxiliary cards (SPST) are used.

Transfer function

Gain Reset filterDeadband Lead/Lag(1) Lead/Lag(2) Lead/Lag(3) Limiter

Inductor Electromagnetic pick-up

Speed detection card

Speed detection Torsional oscillation filtersto PSS functions

4 steps

Design of PSS Parameters

Site Commissioning test of PSS

Calculation of damping torque :

M : inertia

Ms2+Ns+WKs2+Ds+W

5 6

Mitsubishi Power System Stabilizer (PSS)

AnalogueAnalogueAnalogue

DigitalDigital

Speed Detectionin Input Type

2MT

P2P1

nD =

The dimensions of the analogue PSS are 250 x 680 x 480mm (LxWxD). Each unit is equipped with thefollowing devices:

The functions of the digital PSS are realized through the software. Generally, computations are performedin the same CPU as the digital AVR. The basic functions are the same as for analogue. Minor differencesare as follows:(1) Fault detection: for analogue, excessive PSS output is detected. However, in the case of the digital unit,

a fault occurring in individual parts (e.g., reset filter) is not realistic. Therefore, rather than basing faultdetection on computation results, a self-diagnostics function is built into the hardware and software todetect faults.

(2) Lag: analogue units have a lag circuit at the final stage that suppresses the noise signal. Generally,this is not incorporated in digital units since noise suppression is carried out at the point of input-signaldetection.

The generator speed is detected by the input type PSS. It is necessary for the PSS speed detectorto be able to detect very small fluctuations with high accuracy. Mitsubishi Electric developed a highlyaccurate, high-performance speed detector (16-bit resolution, 0.05% accuracy) and a filter to eliminatetorsional oscillation in the spinning component.

An appropriate parameter design is very important in order for a PSS to operate effectively. In general, theseparameters are set with the single machine infinite bus model; however, on request, analysis using amulti-system model is also available.

During site examination, to confirm the effectiveness of the PSS, power fluctuations are generated when thePSS is in use and when it is not in use, and damping measurements are compared. As a common method forgenerating power fluctuations, a generator voltage transient response test, is applied. In order to quantify theeffectiveness of the PSS, the damping torque is calculated from the test results. Generally, in the case ofapplying a local mode, the PSS is judged to be sufficiently effective if the damping torque is tenfold higher as aresult of using the PSS.

Filter :

Integral of Accelerating Power Type PSS (Power System Stabilizer)

time (sec)

Pow

er

AVR without PSS

Step respnse of voltage reference

AVR with PSS

time (sec)

Pow

er

AVR without PSS

AVR with PSS

Power system fault(1 line open after 3 phases grounding)

A POWER SYSTEM STABILIZER (PSS), which is installed in the Automatic Voltage Regulator of a Generator, can improve power system stability. The PSS has excellent cost performance compared to other power system modifications or additions. MITSUBISHI "Integral of Accelerating Power Type PSS" conforms to Type PSS2A in "IEEE Std. 421.5-1992".

Integral of Accelerating Power Type PSS

The relation of change among mechanical power, electrical power, accelerating power and rotor speed can be illustrated as Fig.1 from the swing equation where the integral of accelerating power is equal to rotor speed.

Thus, Integral of mechanical power is derived as the following equation from measured electrical power and rotor speed (or frequency).The resultant block diagram of sensing input signal can be illustrated as Fig.2. Thus, the input signal of "Integral of Accelerating Power Type PSS" is equivalent to rotor speed.

Where, F(s) is transfer function of the filter for attenuating the torsional oscillation.

Mechanical Power

Electrical Power

Accelerating PowerRotor Speed

M=2H:Inertia constant Fig.1

Fig.2Ms

M

1

1

M1

F(s) Equivalent rotor speed signal

Pmdt

Pedt

Ms1

*Kinds of Speed signal

Configuration of PSS Function

Mitsubishi Integral of Accelerating Power Type PSS (Power System Stabilizer)

(1) Frequency of terminal voltage.....only terminal voltage(2) Frequency of internal voltage calculated from terminal voltage and current (Vi=Vg+xd lg).....(option)(3) Actual rotor speed.....required speed detector, toothed wheel mounted on generator shaft and pickup (option)

Parameters

Parameter DescriptionWash-out Time constant-1Wash-out Time constant-2Wash-out Time constant-3Wash-out Time constant-4Lead Time constant-1Lag Time constant-1Lead Time constant-2Lag Time constant-2Lag Time constantIntegral Time constantRamp-tracking time constantFilter time constantLead Time constant-3Lag Time constant-3Lag Time constant-4PSS GainGainGainInteger filter constantInteger filter constantPSS output limiter "max"PSS output limiter "min"

UnitsSec.Sec.Sec.Sec.Sec.Sec.Sec.Sec.Sec.Sec.Sec.Sec.Sec.Sec.Sec.pu/pupu/pupu/pu

IntegerInteger

pupu

Typical range1 to 10.1 to 10.1 to 10.1 to 10.

0. & 0.02 to 2.0. & 0.02 to 2.0. & 0.02 to 2.0. & 0.02 to 2.0. & 0.02 to 2.

0.5 to 10.0. & 0.02 to 2.0. & 0.02 to 2.0. & 0.02 to 2.0. & 0.02 to 2.0. & 0.02 to 2.

0.2 to 20.0.1 to 5.0.5 to 2.1 to 51 to 5

0. to 0.20. to -0.1

Remarks

Integral of Pe

Normally = T7/2H(Inertia)Normally = 1

Tw1Tw2Tw3Tw4T1T2T3T4T6T7T8T9T10T11T12Ks1Ks2Ks3MN

VSTMAXVSTMIN

Transfer Function of PSS

To AVR

Pe

Vg

1 : Added to PSS2A model2 : If generator voltage is continuosly kept higher than 105% or lower than 95% of rated voltage, generator voltage is automatically reduced within 95 to 105% by changing limit value after time delay.

sTw11+sTw1

sTw21+sTw2

11+sT6

(1+sT8)(1+sT9)M

N

Ks21+sT7

sTw41+sTw4

1+sT11+sT2

1+sT31+sT4

1+sT10 11+sT11 1+sT12

Limiter

Ks1

Ks3

VSTMIN

VSTMAX

sTw31+sTw3

(option)

Pmdt = Pedt +M

Electrical Power(Pe)

Terminal Voltage(Vg)

Wash-out

Wash-out Integral

Lead/Lag

Filter

LimiterTo AVR

Gain

Frequency

Step-up Transformer

Rotor Speed

TransducerPick Up

Vg,Ig

PTCTG

or

(option)

New Publication, effective Sep. 2001.Specifications subject to change without notice.

HEAD OFFICE: MITSUBISHI DENKI BLDG., MARUNOUCHI, TOKYO 100-8310. TELEX: J24532 CABLE: MELCO TOKYO

Improper use of products can cause severe injury or death,and may result in damage to product and other property.Please read instruction manual before installing or using product.

SE-D779-A(0109-0.5)MDOC

Mitsubishi Integral of Accelerating Power Type PSS (Power System Stabilizer)

AVR

AVR+

PSS

K1

K1+K1A

K1A+DA

K1+D

K1+D

K1+K1A+K1P

1Ms

1Ms

1Ms

S

S

S

D 0

0

0

D+DA

D+DA+DP

Theory of PSS

Though a generator output power is decided by the turbine mechanical torque, a generator output power also can be changed by changing excitation value transiently. (Fig.3) A PSS detects the changing of generator output power, controls the excitation value, and reduces the power swing rapidly. (Fig.4)

Generator output power

Excitation value

Generator output power

Excitation value

Constant Excitation

Block Diagram Torque Characteristics

K1 : Synchronizing TorqueD : Damping TorqueM : Inertia

K1A : Synchronizing Torque by AVRDA : Damping Torque by AVR

K1P : Synchroning Torque by PSSDP : Damping Torque by PSS

(Damping Torque)

(Synchronizing Torque)

Resultant Torque

Resultant Torque

By changing of excitation value,generator output power can be changed transiently

(Fig.3) (Fig.4)

A PSS detects the changing of generator output power, controls the excitation value, and reduces the power swing rapidly.

Summary

Explanation on torque vector

(Stable at D+DA+DP 0)

(Unstable at D+DA 0)

C8641-A_Power_System_Stabilizer(1).pdfD779-A_Power_System_Stabilizer(2).pdf